Underwater thermal connector assembly

ABSTRACT

An underwater thermal connector has mating plug and receptacle units configured for releasable mating engagement to form a sealed thermal connection for transferring heat into or out of subsea equipment housing and pipe lines. The receptacle unit has an inner chamber containing thermally conductive media and having a forward end opening which is sealed in the unmated condition, an outer thermally insulating chamber surrounding the inner chamber, a first thermal contact in the inner chamber, and a thermal conductor or heat pipe communicating with the first thermal contact and extending out of an outer end of the unit. The plug unit has at least one thermal conductor or heat pipe having an outer end and extending forward through a rear manifold and terminating in a thermal contact pin which engages the first thermal contact when the units are in mating engagement.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e) of co-pending U.S. Provisional Patent Application No. 62/200,552 filed on Aug. 3, 2015, the contents of which are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to connector assemblies having releasably mateable plug and receptacle units designed for use underwater or in other hostile environments, and is particularly concerned with an underwater thermal connector assembly for connection of heat pipes rather than electrical conductors or optical fibers.

2. Related Art

There are many types of submersible connectors for making electrical and fiber-optic cable connections in hostile environments. One type includes connectors for sealed subsea mating and de-mating. Such underwater connectors typically comprise a plug unit containing one or more contact probes and a receptacle unit containing an equivalent number of receptacle contacts or junctions for engagement with the contact probes, which extend into the receptacle unit when the units are connected together. Typically, the contacts or junctions are contained in a sealed chamber containing dielectric fluid, and the probes enter the chamber via one or more normally sealed openings. In U.S. Pat. No. 5,645,442 of Cairns, a submersible fluid-filled electrical connector has a receptacle with a contact chamber sealed with a stopper or plunger, and a plug for mating engagement with the receptacle has a conductive pin which engages through a sealed opening and pushes the plunger back to engage with a contact socket in the receptacle.

SUMMARY

Apparatus and methods for isolated thermal connection between heat pipes in a subsea environment are provided. In one aspect, an underwater thermal connector comprises plug and receptacle (male and female) units configured for releasable mating engagement to form a thermal connection. The receptacle unit has a rear end and a forward end and includes at least one thermal contact chamber containing thermally conductive media and having a sealable forward end opening, a heat pipe having a first end extending into the contact chamber and in thermal communication with a contact socket in the chamber and a second end communicating with a thermal interface at the rear end of the receptacle unit, and a thermally insulating shuttle piston extending through the contact socket and having a forward end in sealing engagement with the forward end opening. The plug unit has at least one thermal interface at a rear end of the unit, a thermally insulating manifold having at least one through bore, and at least one heat pipe extending forward from the thermal interface through the at least one through bore and terminating in a thermal contact pin extending forward from the manifold. The thermal contact pin is configured for sealing engagement through the forward end opening of the contact chamber in the receptacle unit on mating engagement of the units, and urges the shuttle piston inward through the contact socket such that the contact pin is received and directly engaged by the contact socket when the units are in mating engagement, effecting thermal connection between the heat pipes in the two units.

In one embodiment, the receptacle unit has one contact chamber containing a plurality of contact sockets aligned with respective openings in a forward end wall of the chamber, and a corresponding number of heat pipes extending into the sockets in thermal communication with the respective contact sockets. Alternatively, there may be plurality of separate contact chambers each containing one heat pipe and contact socket and having a forward end opening in which a forward end of a respective shuttle piston is sealed in the unmated condition of the units.

The underwater thermal connector may be used for various subsea equipment applications, for example heat rejection from subsea components such as VFDs (variable frequency drive motor controller), power electronics, transformers, and motors; heat source and sink for thermal electric generators, and for heat transfer for thermal storage and injection during well shut in and start up.

Other features and advantages of the present invention should be apparent from the following description which illustrates, by way of example, aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of the present invention, both as to its structure and operation, may be gleaned in part by study of the accompanying drawings, in which like reference numerals refer to like parts, and in which:

FIG. 1 is a schematic illustration of a heat pipe;

FIG. 2 is a side elevation view, in partial section, of a female or receptacle unit of one embodiment of an underwater thermal connector assembly;

FIG. 3 is a side elevation view, in partial section, of a male or plug unit of the underwater thermal connector assembly designed for releasable subsea mating engagement with the receptacle unit of FIG. 2;

FIG. 4 is a side elevation view, in partial section, of the plug and receptacle units of FIGS. 2 and 3 in the mated condition;

FIG. 5 is a cross-sectional view illustrating one embodiment of the thermal conductor assembly of FIGS. 2 to 4 forming a thermal connection for transferring heat out of a subsea electronics or equipment housing; and

FIG. 6 is a cross-sectional view illustrating an embodiment of the thermal conductor assembly of FIGS. 2 to 4 forming a thermal connection for transferring heat out of a subsea liquid or gas carrying pipeline.

DETAILED DESCRIPTION

Certain embodiments as disclosed herein provide for an isolated thermal connection between heat pipes in a subsea or other hostile environment.

After reading this description it will become apparent to one skilled in the art how to implement the invention in various alternative embodiments and alternative applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this detailed description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention.

FIG. 1 is a schematic illustration of a heat pipe 10 for transfer of heat between two interfaces at different temperatures T1>T2. Heat pipe 10 comprises an outer shell 19 having opposite ends 12, 16, an annular wick 18 of suitable wicking material extending along the inside of shell 19 between the ends, and an interior lumen 15 inside wick 18. At the hot or heat source end 12 of the heat pipe, a liquid in contact with the thermally conductive end face 14 at temperature T1 absorbs heat so that it evaporates and turns into a vapor which travels along the interior lumen 15 of the tube towards the colder or heat sink end 16 of the heat pipe at temperature T2. The vapor is condensed back into a liquid at the colder end of the pipe extending up to end face 17, releasing the latent heat. The liquid then returns to the heat source end of the pipe via annular wick 18 surrounding the inner lumen 15, and the cycle repeats to transfer thermal energy from one end of the pipe to the other. The direction of heat transfer is reversed if T1 is lower than T2 (T1<T2).

FIGS. 2 to 4 illustrate one embodiment of an underwater thermal connector assembly 20 shown in the mated condition in FIG. 4. In the mated condition, connector assembly 20 is designed to transfer heat into or out of subsea equipment, as described in more detail below. FIG. 2 illustrates the receptacle or female unit 22 of the connector assembly, while FIG. 3 illustrates the mating plug or male unit 24 of the assembly. The connector assembly is similar to prior underwater electrical connectors as described in U.S. Pat. Nos. 5,645,442 and 7,959,454, the contents of which are incorporated herein by reference, but electrical conductors are replaced by high thermal conductivity heat pipes, conductive materials are replaced by thermally conductive materials, and electrically insulating materials are replaced by thermal insulating materials.

In this embodiment, the female connector unit 22 comprises a housing or shell 25 which may be made of a relatively low thermal conductivity metal such as titanium or 316 stainless steel, and one, two or more socket assemblies 26 (one of which is visible in FIG. 2) extending from the rear or outer end 27 towards the forward or inner end 29 of shell 25. Although plural socket assemblies 26 are illustrated, a single socket assembly may be provided in other embodiments, depending on heat transfer requirements. Shell 25 has a through bore 28, a base or stopper 30 secured in a rear or outer end portion of through bore 28, and a forward or inner end wall or plate 31 having openings 32 aligned with respective socket assemblies 26. Base or stopper 30 is of rigid thermal insulating material such as Ultem™, PEEK™ or the like. An outer bladder 33 extends from the rear end wall 30 through bore 28 and has a forward or inner end seal 34 behind end plate 31 having a plurality of sealable openings each aligned with a respective opening 32 in forward end plate 31. Each socket assembly 26 comprises a heat pipe 36 having a rear or outer end 83 thermally connected to external thermal interface 38, shown schematically in FIG. 2. Heat pipe 36 extends from interface 38 through an aligned bore 40 in end wall or stopper 30 and into the shell. Where there is more than one heat pipe 36 in the connector unit, each heat pipe may terminate at a separate thermal interface 38, or all heat pipes may terminate to the same thermal interface. Heat pipe 36 is similar to heat pipe 10 of FIG. 1, and has an inner lumen 80 surrounded by an annular wick 82 extending along the length of heat pipe 36 between thermally conductive end walls 83, 84. End wall 84 is in thermal communication with socket 44 via thermally conductive sleeve 42.

A thermally conductive sleeve 42 extends from the forward or inner end of heat pipe 36 towards the inner end of the shell, and terminates at a thermal contact socket 44 of thermally conductive material. Sleeve 42 may be in thermal contact with inner or forward end 84 of heat pipe 36 or may be formed integrally with the inner end of heat pipe 36, and may be an annular extension of the heat pipe. A thermally insulating shuttle piston 45 of Ultem™, PEEK™ or the like extends slidably through the contact socket 44 and has a forward end in sealing engagement in one of the sealable openings 37 in the forward or inner end wall or seal 34 of outer bladder 33 in the unmated condition of FIG. 2. Piston 45 is biased into the extended position of FIG. 2 by spring 46 which acts between inner end 84 of heat pipe 36 and an adjacent end of shuttle piston 45. In one embodiment, the sleeve 42 and contact socket 44 are of a suitable thermally conductive material such as copper.

Socket assembly 26 also includes an outer bladder 48 of flexible thermal insulating material such as flexible elastomer material extending from the forward end wall 34 of outer bladder 33 rearwards over the shuttle piston 45, contact socket 44, and sleeve 42 up to the inner end 84 of heat pipe 35. Bladder 48 may be formed integrally with the forward end wall 34 of bladder 33. Inner chamber 50 within bladder 48 communicates with the interior of sleeve 42 via opening 51, and may be filled with a mobile thermally conductive medium such as the synthetic ester Midel® 7131, manufactured by M&I Materials Limited of Manchester UK, or other high thermal conductivity transformer fluid. A second chamber 53 is formed between bladders 48 and 33 and contains a mobile thermal insulating medium such as Dow Corning 200 or the like, and a third, outer chamber 52 is formed outside bladder 33 and exposed to the surrounding medium via ports 54 in shell 25, for pressure compensation purposes during mating and de-mating. Bladder 48 has an annular inner rib 55 secured to contact socket 44, and has one or more inwardly directed annular nibs 56 between ribs 55 and end wall 34 which are in sealing engagement with the outer surface of shuttle piston 45 in the unmated condition of FIG. 2.

Plug unit 24 of FIG. 3 has an outer cylindrical shell 60 which is of the same material as shell 25, for example relatively low thermal conductivity metal such as titanium or 316 stainless steel. Shell 60 has a through bore 62 and a rear portion in rotating engagement with rear or outer manifold 64 which has a forwardly extending sleeve, and one or more plug probes or pins 65 which extend through bores in rear manifold 64 into hollow forward or inner end portion 66 of the plug through bore. Each plug probe 65 is a high thermal conductivity heat pipe of similar or identical construction to the heat pipe 10 of FIG. 1 and heat pipe 65 has an inner lumen 85 surrounded by annular wick 86 extending from thermally conductive rear or outer end wall 88 to forward or inner end 70 of the heat pipe. In one embodiment, the heat pipes 40 and 65 are copper. Rear end wall 88 is terminated at a thermal interface 68 (shown schematically in FIG. 3). Forward or inner end or tip 70 of heat pipe 65 is spaced inward from the forward end 72 of plug shell 60 and also comprises a thermal interface. Manifold 64 is also formed of a suitable rigid thermal insulating material such as Ultem™, PEEK™ or other rigid thermoplastic material. The hollow forward end portion 66 is of larger diameter than a corresponding forward end portion 74 of the receptacle manifold so that portion 74 is slidably engaged inside forward end portion 66 as the two parts are brought into engagement. Internal screw threads 75 at the forward or inner end of bore portion 66 are designed for threaded engagement with external screw threads 76 on the outer surface of receptacle shell 22 to secure the parts together in the mated condition of FIG. 4.

Thermal interfaces 38 and 68 are shown schematically in FIGS. 2 and 3. In practice, one of the interfaces is in communication with a heat sink which may be provided by deep seawater surrounding a subsea equipment installation or wellhead, or a heat rejection connector on a vessel or surface installation such as an oil rig. The other interface is in communication with a heat source, such as subsea components in a subsea equipment housing, for example VFDs, power electronics, transformers, and motors, or an oil pipe where oil flowing through the pipe is the heat source. Heat transfer from the thermal interfaces to the heat sources and sink is accomplished using conventional heat transfer systems. This is includes direct conduction heat transfer, passive convective heat transfer with extended surface fins, circulating fluid systems and heat pipes. If interface 38 is the heat source and interface 68 is the heat sink, then T1 (temperature at end 83 of heat pipe 36) is greater than T2 (temperature at end 84 of heat pipe 36), and heat flux direction is from 83 to 84 or left to right as viewed in FIG. 4. For the heat pipe in plug 24, T1 (at outer end 88 of heat pipe 65) is less than T2 (temperature at end 70), and the heat flux direction is towards interface 68. These directions are reversed if interface 68 is the heat source and interface 38 is the heat sink.

In the embodiment illustrated in FIG. 4, the receptacle is mounted in a threaded opening or port in a wall or pressure barrier 90 of a subsea pressure vessel or other enclosure, as indicated in dotted outline in FIG. 2 and FIG. 4. In this embodiment, thermal interface 38 communicates with one or more heat sources inside the enclosure, and the parts of connector 20 outside the enclosure are surrounded by the seawater environment forming a heat sink, while thermal interface 68 of plug unit 24 communicates directly or indirectly with the heat sink for heat transfer out of the equipment housing or subsea pressure vessel. In other embodiments, the heat pipes and thermal interfaces may alternatively be configured for heat transfer into the equipment housing, or the thermal interface 38 at the opposite end of the connector may be surrounded by seawater.

In order to connect the units, the forward ends of the receptacle and plug units are first aligned, and the hollow forward end portion 66 of plug shell 60 is engaged over the forward end portion 74 of receptacle unit 25. The forward ends 70 of plug pins 65 enter the aligned openings 32 in the receptacle shell end plate or wall 31 and engage the forward ends of shuttle pistons 45, pushing the pistons inward and compressing return springs 46. As the receptacle unit continues to be advanced into plug shell 60, the shuttle pistons are retracted inward from contact sockets 44, and the contact pins or heat pipes 86 move into sealing engagement with sealable openings 37 in place of shuttle pins 45, while the tips 70 of contact pins or heat pipes 65 move into thermal engagement with the respective sockets 44. This effectively connects heat pipes 35 and 65 together in series via a thermal connecting portion comprising sleeve 42 and socket 44 between the forward or inner ends 70, 84 of the heat pipes.

FIGS. 5 and 6 illustrate some embodiments or examples of the thermal connector assembly 20 of FIGS. 2 to 4 with different thermal interfaces 38 and 68 and heat sources. It will be understood that different heat sources or heat sinks may be connected via the thermal connector assembly in other embodiments. In the embodiment of FIG. 5, the thermal interface 38 at the outer ends of heat pipes 80 of receptacle or female connector unit 22 comprises a subsea housing or enclosure 95 of thermally conductive material having an internal chamber 96 holding electronics 97 or other heat generating equipment on thermally conductive mount 91. Chamber 96 may be a gas filled one atmosphere chamber as known in the field. The thermal interface 68 at the opposite end of assembly 20 comprises a finned heat exchanger 98 which is thermally coupled to the outer ends 88 of heat pipes 85 of the plug or male connector unit 24. The finned heat exchanger 98 is surrounded by the seawater environment which acts as the heat sink.

In the embodiment of FIG. 5, T_(enclosure) equals the temperature of the electronics equipment or heat source 97 inside electronics housing 95 and T_(seawater) is the temperature of the seawater or heat sink surrounding the heat exchanger 98, and T_(enclosure)>T₁>T₂>T_(seawater), where T₁ is the temperature at the outer ends 83 of heat pipes 80 and T₂ is the temperature at the outer ends 88 of heat pipes 85.

FIG. 6 illustrates an embodiment in which thermal connector assembly 20 communicates between a heat source comprising oil or petroleum liquid or gas carried by pipe 100 from an underwater well, and a heat sink comprising sea water surrounding the opposite end of the assembly. Pipe 100 has an outer, thermally insulating layer 105 and an inner layer 104 of thermally conductive material comprising thermal interface 38. The oil or gas travels along the interior 102 of pipe 100. Thermal interface 38 is formed between the outer end portion of connector unit 22 and the inner, thermally conductive pipe layer 104. As illustrated, the outer ends 83 of the heat pipes 80 of unit 22 extend through the insulation layer 105 and terminate in thermally conductive layer 104.

The thermal interface at the outer end of connector unit 24 is surrounded by seawater, and comprises connector or adapter 106 of thermally conductive material in which the outer ends 88 of heat pipes 85 are terminated, a thermoelectric generator or thermopile 108 suitably connected to connector or adapter 106 on one side, and to a finned heat exchanger 110 on the other side. Thermoelectric generator 108 has an electric power output 112 which may be connected to a subsea power cable or the like.

In the embodiment of FIG. 6, T_(liquid)>T₁>T₂>T_(seawater), where T_(liquid) is the temperature of oil or liquid carried in pipe 100 (heat source).

This arrangement permits releasable mating engagement between heat pipes in subsea mateable thermal connector units, while maintaining a seal against seawater ingress into the receptacle unit both in the mated and unmated conditions of the units. This allows heat to be transferred more easily into or out of subsea equipment. The underwater mateable thermal connector described above is configured to maintain thermal conduction while reducing or minimizing convection heat losses by means of suitable thermal insulating materials used in the connector units. The connector may be used for heat rejection from subsea components such as variable frequency drives or motor controllers, power electronics, transformers and motors as used in the subsea oil and gas industry and from oil or gas traveling along a subsea pipeline, as well as in other subsea applications such as communication systems, and for use as a heat source and sink for thermoelectric generators, as well as to provide for heat transfer for thermal storage and injection during well shut in and start up. The thermal connector assembly may also be used for heat transfer in other harsh environments.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein can be applied to other embodiments without departing from the spirit or scope of the invention. Thus, it is to be understood that the description and drawings presented herein represent a presently preferred embodiment of the invention and are therefore representative of the subject matter which is broadly contemplated by the present invention. It is further understood that the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and that the scope of the present invention is accordingly limited by nothing other than the appended claims. 

What is claimed is:
 1. An underwater thermal connector, comprising: a plug unit having an outer shell having a forward end and a rear end, an inner thermally insulating manifold, and at least one first thermal conductor comprising a pin extending through the thermally insulating manifold and having a forward end portion that projects in a forward direction from the thermally insulating manifold and has a first thermal contact at its forward end; a receptacle unit having an outer shell having a forward end and a rear end, at least one contact chamber inside the shell containing a thermally conductive medium, and at least one second thermal contact in the contact chamber configured for thermal engagement with the first thermal contact in a mated condition of the units; at least one second thermal conductor in communication with the second thermal contact and extending from the contact chamber out of the rear end of the outer shell of the receptacle unit; the plug and receptacle units being movable between an unmated condition and a mated, sealed condition in which they are in releasable mating engagement and the first and second thermal contacts are in thermally conductive communication; and the contact chamber having a sealable forward end opening through which the pin extends in the mated condition of the units, the sealable forward end opening sealing against the pin in the mated condition of the units.
 2. The connector of claim 1, wherein the first and second thermal conductors comprise heat pipes, each heat pipe having a forward end inside the respective plug and receptacle units and a rear end comprising a thermal interface, one of said thermal interfaces communicating with a heat source and the other thermal interface communicating with a heat sink.
 3. The connector of claim 1, wherein the thermally conductive medium in the contact chamber is a fluid and a compliant member of thermal insulation material surrounds said contact chamber and has a forward end wall in which said sealable forward end opening is located, said compliant member flexing to compensate for pressure and volumetric variations within said contact chamber.
 4. The connector of claim 1, wherein the second thermal contact comprises a contact socket and the receptacle unit further comprises a shuttle piston of thermally insulating material extending in a forward direction through the contact socket and being movable between a retracted position inside the contact chamber in the mated condition of the units and an advanced position in which the forward end is sealably engaged in the forward end opening of the contact chamber and the shuttle piston and the forward end opening form a forward end seal in the unmated condition of the units.
 5. The connector of claim 4, further comprising a biasing member urging the shuttle piston into sealing engagement with the forward end opening of the contact chamber in the unmated condition of the units.
 6. The connector of claim 5, wherein the forward end portion of the first thermal conductor is configured to extend through the forward end opening of the contact chamber and urge the shuttle piston into the retracted position in the mated condition of the units, the first thermal contact engaging in the contact socket and the first thermal conductor being in sealing engagement with the forward end opening of the contact chamber in the mated condition of the units.
 7. The connector of claim 1, wherein the plug unit has two or more first thermal conductors comprising pins extending through the thermally insulating manifold, each pin having a respective first thermal contact at a forward end of the respective pin, and the receptacle unit has two or more second thermal contacts and a corresponding number of second thermal conductors in communication with respective second thermal contacts, each first thermal contact being positioned for alignment and mating engagement with a respective second thermal contact in a mated condition of the units.
 8. The connector of claim 7, wherein each thermal conductor comprises a heat pipe having a thermal interface located outside the rear end of the respective plug or receptacle unit.
 9. The connector of claim 1, further comprising a second chamber containing thermal insulating media surrounding the first chamber, the second chamber having a second outer peripheral wall of compliant, thermally insulating material.
 10. The connector of claim 9, further comprising a third chamber surrounding the second chamber between the second outer peripheral wall and outer shell of the receptacle unit, the outer shell having at least one port communicating with the third chamber whereby the second outer peripheral wall is exposed to the surrounding medium via the port for pressure compensation purposes.
 11. The connector of claim 1, wherein the outer shells of the plug and receptacle units are of low thermal conductivity metal.
 12. A subsea thermal connector assembly, comprising: a thermal connector having opposite first and second ends and comprising first and second connector units movable between an unmated condition and a mated condition in which they are in releasable mating engagement, each connector unit having a forward end and a rear end, the forward end facing the forward end of the other connector unit during mating engagement of the units; the first connector unit having an outer shell, an inner thermally insulating manifold, and at least one first thermal conductor comprising a pin extending through the thermally insulating manifold and having a forward end portion that projects forwards from the thermally insulating manifold and has a first thermal contact at its forward end; the second connector unit having an outer shell, at least one contact chamber inside the shell containing a thermally conductive medium, at least one second thermal contact in the contact chamber configured for thermal engagement with the first thermal contact in a mated condition of the units, and at least one second thermal conductor in communication with the second thermal contact and extending from the contact chamber out of the rear end of the outer shell of the second connector unit; the contact chamber having a sealable forward end opening through which the pin extends in the mated condition of the units, the sealable forward end opening sealing against the pin in the mated condition of the units; the first and second thermal conductors each having at least one outer thermal contact at an outer end of the respective the thermal connector unit; a first thermal interface for communication with a heat sink and connected to the at least one outer thermal contact at one of the ends of the thermal connector and a second thermal interface for communication with a heat source and connected to the at least one outer thermal contact at the other end of the thermal connector.
 13. The assembly of claim 12, wherein the first thermal interface is a finned heat exchanger and the heat sink comprises a subsea environment surrounding the heat exchanger.
 14. The assembly of claim 13, wherein the first thermal interface includes a thermoelectric generator and the heat sink comprises a subsea environment surrounding the heat exchanger.
 15. The assembly of claim 12, wherein the second thermal interface is a wall of a subsea electronics housing and the heat source comprises heat generating components inside the subsea housing.
 16. The assembly of claim 12, wherein the second thermal interface is a subsea pipe for transport of a fluid medium comprising petroleum liquid or gas from a subsea well, and the heat source comprises the fluid medium.
 17. The assembly of claim 12, wherein the first and second thermal conductors comprise heat pipes.
 18. A method of transferring heat into or out of subsea equipment, comprising: thermally connecting a first thermal interface at a rear end of a first heat pipe in a first connector unit of a releasably mateable subsea thermal connector to a heat source or sink, the first connector unit having a sealable opening which communicates with a thermal contact chamber inside the first connector unit and is sealed in an unmated condition of the first connector unit; and releasably mating a second connector unit with the first connector unit, the second connector unit containing a second heat pipe having a forward end contact and configured for sealing engagement through the sealable opening in the first connector unit into the thermal contact chamber during mating of the units, wherein the second heat pipe communicates with a second thermal interface at its rear end which is in communication with a heat sink or a heat source; and a forward end contact of the second heat pipe is in thermal communication with a forward end of the first heat pipe in the mated condition of the units.
 19. The method of claim 18, wherein the subsea thermal connector extends through a wall of a subsea housing, the heat source comprises heat generating electronic equipment inside the subsea housing and the heat sink comprises seawater surrounding the subsea housing.
 20. The method of claim 18, wherein one of the thermal interfaces comprises a subsea pipe carrying petroleum liquid or gas from a subsea well, and the heat source comprises petroleum liquid or gas from a subsea well travelling through the pipe.
 21. The method of claim 18, wherein the second thermal interface comprises a finned heat exchanger or a thermoelectric generator. 